Process for producing images



United States Patent PROCESS FOR PRODUCING IMAGES Rene Robert Zemp, Scotch Plains, N. .L, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application November 8, 1954, Serial No. 467,630

19 Claims. (Cl. 95--7) This invention is concerned with light-sensitive photo graphic elements and with a process for producing images, including relief images, which utilize such elements. More particularly it relates to a process of preparing printing reliefs utilizing such elements. Still more particularly it is concerned with a process for making printing reliefs in hardened protein layers containing diazonium salts which yield certain hydroxyaromatic acids, and to light-sensitive photographic elements useful therein.

An object of this invention is to provide new lightsensitive photographic elements, e. g. films, plates and papers which are useful in preparing relief images, in-

eluding printing reliefs. Another object is to provide a simple and practical process for making relief images. Another object is to provide a process of preparing such images which does not require the use of light-sensitive silver salts. Yet another object is to provide such a process which will produce a practical relief image in a relatively short time. A further object is to provide such a process which utilizes light-sensitive diazonium salts. A still further object is to provide such a process which results in printing reliefs. Still other objects will be apparent from the following description of the invention.

The light-sensitive or photographic elements of this invention comprise a flexible or rigid support, e. g., a sheet, plate, film or paper etc., that has superposed on at least one surface thereof, either directly or by means of one or more sublayers, a layer of hardened protein colloid containing a light-sensitive diazonium salt which decomposes under the influence of actinic light of wavelengths from 2000 to 3900 A. to form an o-hydroxyaromatic acid of the benzene and naphthalene series, said salt being present in an amount of at least 0.1 part per 100 parts, by weight, of protein colloid.

The support may be flexible or rigid and composed of any of the conventional materials used in making photographic elements. Thus, it may be a sheet or plate of metal, e. g., copper, brass, zinc, iron, steel, aluminum, magnesium alloy etc. or composed of a hydrophobic film, including a cellulose derivative, e. g., cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose propionate, cellulose nitrate, etc; a super polymer, e. g., nylon, polyvinyl chloride, poly-(vinyl chloride co vinyl acetate), polystyrene, polyester, e. g., polyethylene terephthalate, or cardboard, laminated paper, etc. in the case of fibrous supports such as paper or cardboard the surface may be coated with resins, or polymeric materials as described above.

Various types of sublayers may be used between the surface of the support and the layer of hardened protein containing the diazonium. salt. in general, any of the materials which have been used as sublayers in photographic films, plates and papers having gelatin silver halide emulsion layers or polyvinyl acetal silver halide emulsion layers can be used to anchor the hardened protein colloiddiazonium salt layers of this invention to the support. The particular sublayer used will depend upon the particular character of the support. For example, with cellulose organic acid ester supports, nitrocellulose or the vinylidene chloride copolymers described in Alles and Saner U. S. P. 2,491,023 are useful, and with polyester supports, the vinylidene chloride-acrylic ester-itaconic acid copolymers of Alles and Saner 2,627,088 are useful.

The sublayers may contain an anti-'halation dye or pigment which absorbs light of wavelengths to which the diazonium salt is sensitive. In the case of transparent supports, an antihalation layer can be placed on its rear surface. It is generally advisable to have a gelatin sublayer between the nitrocellulose, resin or copolymer sublayer and the protein-diazonium salt layer.

The novel processes of this invention, in their broader aspects, comprise exposing to actinic light of wave lengths from 2000 to 3900 A. selected areas of a hardened, waterpermeable reversible protein colloid layer containing a light-sensitive diazonium salt that decomposes under the influence of such light to form an o-hydroxyaromatic acid or the benzene and naphthalene series. When a relief image is desired the layer, or the surface thereof, is removed in the light exposed areas.

The light-sensitive diazonium salts, comprehended by the invention, may be represented by the general formula:

wherein X is the anion of an acid, e. g., Cl, SOF, N03", BFe", SOsNaand 803K, and R is a radical taken from the group having the formulae:

z and wherein Y is a member taken from the group consisting ofH, Cl, Br, N02, NH2, COOH, -alkyl of 1 to 5 carbon atoms and aryl of not more than 10 carbon atoms and Z is a member taken from the group consisting of H, Cl, Br, --NOz, -NH2, -COOH, alkyl of 1 to 5 carbon atoms and aryl of not more than 10 carbon atoms. The groups Y and Z may be in the same or different rings. The remaining positions in the benzene and naphthalene rings have hydrogen atoms attached to nuclear carbon atoms.

Suitable alkyl radicals Y and Z which may be present in the compounds of the above formulae and in the following paragraph include methyl, ethyl, propyl, isopropyl, n-butyl and n-amyl and the suitable aryl radicals include phenyl and naphthyl.

Light-sensitive diazonium salts which have the property of being decomposed by the action of actinic light to form o-hydroxyaromatic acids of the benzene and naphthalene series, as indicated by the above formula, include diazotized anthranilic acid and its 3- and S-alkyl, phenyl and nitro-substituted derivatives, diazotized- Z-amino-l-naphthoic acid and diazotized land 3-amino- Z-naphthoic acids. The salt-forming anion may be any of the anions X which are described above.

The thickness of the light sensitive layer and the amount of salt present therein will depend upon the particular use to which the resulting element will be put. Thus the thickness may vary from 0.05 mil to 100 mils, or more. The amount of salt can vary from 0.1 part to 5.0 or more parts per 100 parts, by weight, of protein colloid.

. In that aspect of the invention which is concerned with the preparation of yplanographic printing plates, the

amount of light-sensitive diazonium salt present in the hardened protein colloid layer may vary from 0.1 to 0.5 part per 100 parts, by weight, of the protein colloid. The exposed areas which. are softened and hydrophilic in character, when wet with water, repel the printing inks used in planographic printing in such exposed areas. The non-exposed areas receive ink and transfer it to the surface to be printed, in a printing operation.

In the case of making relief images, including printing reliefs, the amount of light-sensitive diazonium salt present in the hardened protein colloid layer may vary from 1.0 to 5.0 parts per 100 parts, by weight, of the protein colloid and the exposed and softened areas of the layer are removed. This can be accomplished by washing the layer with water or an aqueous alkaline solution, e; g., dilute aqueous NaOH accompanied, if desired, with brushing. The exposed areas usually will be removed through to the supporting surface.

The exposure of the hardened, water-permeable protein colloid layer to actinic light in selected areas to form an image can be accomplished in various ways, for instance, the light may pass through (1) a process transparency, i. e., an image-bearing transparency consisting of substantially opaque and substantially transparent areas where the opaque areas are of the same optical density, or (2) a cut-out metal or other stencil. This transparency or stencil should be in contact with or in close proximity to the surface of the protein layer, but when a parallel light source is used can be spaced a substantial distance from the layer.

The light-sensitive diazonium salt can be incorporated in the protein colloid coating solution at the time the layer is coated or cast onto a suitable support, or it may be introduced into the layer later, e. g., by impregnating the layer with an aqueous and/or organic solvent solution containing the light-sensitive. diazonium salt. The diazonium salt-protein colloid coating solution may contain fillers or reinforcing agents of small size, e. g., organophilic silicas, bentonites, silica, powdered glass, etc., having a particle size less than 0.4 mil. Coating of the layers can be accomplished by any of the conventional methods of coating gelatin silver halide emulsion layers, etc.

The water-permeable protein colloid, e. g., gelatin, albumin, collagen, etc., can be hardened with an aldehyde, e. g., formaldehyde, par-aldehyde, acetaldehyde, propylaldehyde, crotonaldehyde, furfuraldehyde, pyruvic aldehyde, acrolein, glyoxal, hexamethylenetetramine, trimethylolnitromethane, 2 nitropropandiol 1,3, monomethylolurea, and dimethylolurea, or with an alum, e. g., chrome alum. The processes of this invention are quite effective with aldehyde-hardened proteins and layers which are hardened with mixturesof two, three, or more of such hardening agents, e. g., an aldehyde and an alum. Hardened gelatin layers are preferred.

In following examples o-carboxybenzenediazonium chloride is used as a diazonium salt. It can be prepared as follows:

Preparation of o-carboxybenzenediazonium chloride Anthranilic acid hydrochloride, in an amount of 3.47 grams (0.02 mol) was dissolved in 50 ml. of ethanol and 2 ml. (0.02 mol) of concentrated hydrochloric acid were added. This solution was cooled to C. by external cooling and 3.5 grams (=0.03 mol) of amylnitrite were added slowly enough under stirring so that the temperature of the solution never exceeded +5 C. After the addition of the amylnitrite was completed, the reaction mixture was held for a period of 10 minutes below +5 C. under constant mechanical stirring, and 100 ml. of ether were added to the solution. A white precipitate of o-carboxybenzenediazonium chloride was formed. After filtering, washing with ether, and drying in vacuo at C., 2.82 grams of product were obtained. The compound had a melting point (with decomposition) of 115 C. Upon rapid heating to high temperature the compound deflagrated.

The invention will be further illustrated but is not intended to be limited by the following examples.

EXAMPLE I A sheet of cellulose acetate film bearing a layer of gelatin approximately 16.4 microns thick which had been hardened by means of 3.7 grams of chrome alum and formaldehyde equivalent to 1.85 cc. of a 37 /2% aqueous formaldehyde solution each per 1000 grams of gelatin was treated in orange light with an aqueous solution containing 2 grams of o-carboxybenzenediazonium chloride per 100 cc. of water until the layer was impregnated thoroughly with such solution. After drying the light-sensitive hardened gelatin layer was exposed behind a' photographic positive line transparency to the light of a 100-watt mercury vapor lamp for five minutes at a distance of 30 cm. and then washed with hot water at 70 C. In the exposed areas of the layer the gelatin became white and opaque due to the formation of small nitrogen bubbles during the decomposition of the diazonium compound. This imagewise opacity disappeared with prolonged immersion of the film in water due to escape of the nitrogen bubbles through the swollen and soft gelatin. When the film was rubbed gently with the fingers or a cotton pad during the hot water treatment the gelatin was washed off in the exposed parts, leaving a positive relief image in which the raised areas correspond to the unexposed areas, i. e., to the opaque areas of the original transparency.

EXAMPLE II The procedure of Example I was repeated, except that o-carboxybenzenediazonium sulfate was used as the diazonium salt. It was made by a procedure similar to that described above except in place of the hydrochloric acid there was used 98% sulfuric acid and instead of the anthranilic acid hydrochloride, there was used anthranilic acid. The final relief image was similar to that obtained in Example I.

EXAMPLE III 'A 0.5% by weight aqueous solution of the diazonium salt described in Example I was applied to a hardened gelatin layer coated on a film of cellulose acetate, said layer being obtained as described in Example I, and dried in the dark. After exposure to ultraviolet light behind a photographic positive line transparency for five minutes as in Example I and immersion in hot water (70 C.), a negative relief image was observed, i. e., the raised areas corresponded to the exposed areas of the film, or to the transparent areas of the original transparency.

After drying the film a very weak relief image could still be observed. By treating the film with a dilute dye solution [Phenosafranine (C. I. No. 840) 1:500 aqueous solution] for 30 seconds a visible dye image was obtained due to differential adsorption of the dye to the unexposed (hardened) and the exposed (softened) areas of the gelatin layer.

EXAMPLE IV A gelatin coated cellulose acetate film of the type described in Example I was sensitized with the solution described in that example and dried in the dark. After 5 exposure to ultraviolet light, as described in, Example I, the film. was soaked in a coupling solution containing:

2,3 dihydroxynaphthalene-6rsodium sulfate grams 2 Sodium hydroxide .do 2 Water ,cc 200 The film was left in this solution for a. few minutes until the couplingin the unexposed areas. was complete and a positive blue image was obtained. By bathing in hot water at 70 C., the gelatin was removed in the exposed areas, leaving a positive relief image of blue gelatin on a clear background.

EXAMPLE V EXAMPLE VI The conditions set forth in Example V were repeated except that o-carboxybenzenediazonium sulfate was used instead of o-carboxybenzenediazonium chloride. The resulting relief image was similar to the one described in Example V.

EXAMPLE VII The following solution of hardened gelatin was coated at 50 C. on a white sized paper of photographic grade to form a very thin layer:

Water cc 100 Gelatin grams" 6 Chrome alum (3% by weight aqueous sol.) cc 5 After coating, the layer was treated with a 1% by weight solution of the diazonium salt described in Example VI. After drying at room temperature in the dark, the paper was exposed to the light of a l-watt mercury vapor lamp at a distance of 30 cm. behind a photographic positive line transparency until the originally yellow color of the sensitized paper was bleached in the exposed areas, which required about /2 to 1 minute. The exposed paper was bathed in cold water for several minutes, and then a greasy ink was applied to the surface of the layer with a cotton pad. The surface was then rubbed with a wet soft cloth and a positive image of the original transparency was obtained, i. e., the unexposed (hardened) areas were ink receptive and the exposed (softened) areas were ink repellent.

EXAMPLE VIII Acarefully cleaned granulated zinc plate was coated with a very thin layer of the following solution:

Water cc 100 Gelatin grams 2 Chrome alum (2% sol.) cc

After drying, a 0.5% by weight aqueous solution of diazotized anthranilic acid was applied to the surface of the gelatin layer by means of a cotton pad, the plate was allowed to dry at room temperature and was protected from white light. After two minutes of exposure to ultraviolet light behind a pattern, the plate was treated with warm water for seconds and then with developing ink. This ink was applied to the gelatin surface of the plate by rubbing with a cotton pad. A direct positive image of the original pattern was obtained, due to the difference in ink receptivity of the exposed and unexposed areas of the gelatin layer.

6 EXAMPLE 1x A. sensitizing solution for oifset plates, i. e., a solution containing albumin and ammonium bichromate, was coated on a zinc plate, the layer was dried and uniformly exposed to ultraviolet light, in order to harden the very thin layer. After 10 minutes exposure, the plate was washed for five minutes, treated with a 1% by weight aqueous solution of diazotized anthranilic acid and dried in the dark. The sensitized plate was placed behind and in contact with a pattern which was spaced about 30 cm. from a source of ultraviolet light, then exposed to ultraviolet light for two minutes and a developing ink was applied to the surface of the plate after the manner described in Example VIII. In the exposed areas, the ink could be removed by rubbing under water with a cotton pad. The resulting ink image was a positive one with respect to the original pattern.

Similar results can be obtained by substituting for the benzoic acid-o-diazonium salts of the preceding examples equivalent amounts of diazotized, 3-nitroanthranilic acid, S-nitroanthranilic acid, 3-bromoanthranilic acid, S-bromoanthranilic acid, S-phenylanthranilic acid, l-amino-Z- naphthoic acid, 3-amino-2-naphthoic acid, 4-, 5-, and 6- chloroanthranilic acid, 3-, 4-, and S-bromoanthranilic acid, 3,4-, 3.5-, 3.6-, 4.5-, and 5.6-dichloroanthranilic acid, 3.5-, and 4.5-dibromoanthranilic acid, 3-, 4-, 5-, and 6- nitroanthranilic acid, 3,5-dinitroanthranilic acid, S-chloro-3-nitroanthranilic acid, 5 bromo 3-nitroanthranilic acid, 3-bromo-S-nitroanthranilic acid, 3-, 4-, 5-, and 6- methylanthranilic acid, 5-bromo-3-methylanthranilic acid, 3-bromo-5-methylanthranilic acid, 5 phenylanthranilic acid, 3-aminophthalic acid, Z-aminoisophthalic acid, 2- aminoterephthalic acid, 2 amino 4-methyl-isophthalic acid, l-amino-Z-naphthoic acid, 3-amino-2-naphthoic acid, and Z-amino-l-naphthoic acid.

In general, an exposure period of 15 to 900 seconds is sufiicient for adequate softening of the exposed areas.

The washing treatment may be carried out with the aqueous solution at a temperature of 60 to C. for 1 to 5 minutes.

Thus, any of the conventional light sources which emit substantial amounts of actinic light can be used. Such sources include carbon arcs, mercury vapor arcs, fluorescent lamps with special ultra-violet light-emitting phosphors, argon glow lamps and photographic flood lamps. Mercury vapor arcs of the sunlamp type are especially useful.

The relief images made by the foregoing procedures can be used directly for letterpress printing. They can also be used for imbibition printing processes involving dyetransfer.

An important use of the processes of the invention is in the preparation of direct positive offset plates. This procedure has the advantage that it eliminates a step in the conventional method of making offset plates, namely, the step of making the intermediate negative.

Halftone printing plates can be readily prepared in accordance with the invention. For this. purpose, the original hardened colloid layer, sensitized with the lightsensitive diazonium salt, should be from 3 to 10 mils in thickness. The softening procedure allows the colloid and any material contained in the colloid in the lightexposed areas to be removed through. to the base by the water washing step. This removal can be accelerated by the use of a 0.5 to 5.0% by weight aqueous NaOH solution.

An advantage of the invention is that it provides new and useful photosensitive elements. Another advantage is that the elements are inexpensive, easy to make and have diverse uses. A further advantage is that the invention provides a presensitized material which can be used to prepare a washed-off plate. Another advantage of the invention is that it provides new and practical processes for preparing printing plates.

N--X III N wherein X is the anion of an acid and R is a radical taken from the group consisting of z and Y where Y and Z are members taken from the group consisting of H,COOH, Cl, Br, NO2, -NH2, alkyl of 1 to 5 carbon atoms and aryl of not more than carbon atoms and the remaining nuclear carbon atoms have hydrogen attached thereto.

2. A photographic element as set forth in claim 1 wherein said colloid is gelatin. 7

3. A photographic element as set forth in claim 1 wherein said colloid is albumin.

4. A photographic element as set forth in claim 1 wherein said support is metal.

5. A photographic element comprising a sheet of hydrophobic film base bearing a hardened water-permeable protein colloid layer containing a light-sensitive diazonium salt of the general formula:

COOH

wherein X is the anion of an acid and R is a radical taken from the group consisting of Y Y M and where Y and Z are members taken from the group consisting of H, COOH, Cl, Br, -NOz, NH2, alkyl of 1 to 5 carbon atoms and aryl of not more than 10 carbon atoms and the remaining nuclear carbon atoms have hydrogen attached thereto.

6. A photographic element as set forth in claim 3 V wherein said colloid is gelatin.

7. A photographic element comprising a sheet of hydrophobic film base having a water-permeable protein colloid layer bearing a hardened water-permeable colloid layercontaining a light-sensitive diazonium salt of the gen-- cral formula:

COOH

wherein X is the anion of an acid and R is a radical taken from the group consisting of and where Y and Z are members taken from the group consisting of H, COOH, Cl, Br, NO2, -NH2, alkyl of 1 to 5 carbon atoms and aryl of not more than 10 carbon atoms and the remaining nuclear carbon atoms have hydrogen attached thereto. 7

8; A photographic element as set forth in claim 3 wherein said sheet is composed of polyethylene terephthalate and said colloid is gelatin.

9. The process which. comprises exposing to actinic light of wave lengths from 2000 to 3900 A. selected areas of a hardened water-permeable protein colloid layer containing a light-sensitive diazonium salt of the general formula:

COOH

wherein X is the anion of an acid and R is a radical taken from the group consisting of and where Y and Z are members taken from the group consisting of H, COOH, Cl, Br, NO2, NH2, alkyl of l to carbon atoms and aryl of not more than carbon atoms and. the remaining nuclear carbon atoms have hydrogen attached thereto.

10. The process of making planographic printing plates which comprises exposing to actinic light through an image-bearing transparency a hardened water-permeable protein colloid layer containing 0.1 to 0.5 part by weight per 100 parts by weight of the protein colloid of a lightsensitive diazonium salt of the general formula:

COOH

Ill

wherein X is the anion of an acid and R is a radical taken from the group consisting of and where Y and Z are members taken from thegroup consisting of H, COOH, Cl, Br, NOz, --NH2, alkyl of 1 to 5 carbon atoms and aryl of not more than 10 carbon atoms and the remaining nuclear carbon atoms have hydrogen attached thereto. 1

11. A process as set forth in claim 10 wherein said colloid is gelatin.

12. A process as set forth in claim 11 wherein said diazonium salt is an o-carboxybenzenediazonium salt.

13. A process as set forth in claim 12 wherein said salt is o-carboxybenzenediazonium chloride.

14. The process of making relief images which comprises exposing to actinic light through an image-bearing transparency a hardened water-permeable protein colloid layer containing 1.0 to 5.0 parts by weight per 100 parts by weight of the protein colloid of a light-sensitive diazonium salt of the general formula:

COOH

III

wherein X is the anion of an acid and R is a radical taken from the group consisting of and where Y and Z are members taken from the group consisting of H, --COOH, Cl, Br, -NOz, NH2, alkyl of 1 to 5 carbon atoms and aryl of not more than 10 carbon atoms and the remaining nuclear carbon atoms have hydrogen attached thereto.

15. A process as set forth in claim 14 wherein said colloid is gelatin.

16. A process as set forth in claim 15 wherein said diazonium salt is an o-carboxybenzenediazonium salt.

17. A process as set forth in claim l6 wherein said salt is o-carboxybenzenediazonium chloride.

18. The process of making relief images which comprises exposing to actinic light through an image-bearing transparency a hardened water-permeable protein colloid layer containing 1.0 to 5.0 parts by weight per parts by weight of the protein colloid of a light-sensitive diazonium salt of the general formula:

COOH

wherein X is the anion of an acid and R is a radical taken from the group consisting of i Z Z and 1 where Y and Z are members taken from the group consisting of H, -COOH, Cl, Br, -N0z, NH2, alkyl of 1 to 5 carbon atoms and aryl of not more than 10 carbon atoms and the remaining nuclear carbon atoms have hydrogen attached thereto.

19. A process as set forth in claim 18 wherein said protein colloid is hardened with an aldehyde and an alum.

No references cited. 

1. A PHOTOGRAPHIC ELEMENT COMPRISING A SHEET SUPPORT BEARING A HARDENED WATER-PERMEABLE PROTEIN COLLOID LAYER CONTAINING A LIGHT-SENSITIVE DIAZONIUM SALT OF THE GENERAL FORMULA: 